The effect of chitosan oligosaccharide (COS, 1 kDa<MW<3 kDa) on pro inflammatory cytokines-induced nitric oxide (NO) production and invasiveness of human colorectal adenocarcinoma HT-29 cells was investigated. COS (0.1-5 mg/ml) suppressed the NO production induced by proinflammatory cytokines (100 U/ml IFN-${gamma}$, 10 ng/ml IL-$1{alpha}$, and 25 ng/ml TNF-${alpha}$) in HT-29 cells. Inducible nitric oxide synthase (iNOS) expression induced by these cytokines was inhibited by COS. COS pretreatment inhibited the invasiveness of cytokines-treated HT-29 cells through Matrigel-coated membrane in a dose-dependent manner. COS also inhibited cytokines-induced matrix metalloproteinase (MMP)-2 activity. This study shows that proinflammatory cytokines induce NO production, iNOS expression, and invasiveness of human colorectal adenocarcinoma HT-29 cells. COS pretreatment inhibited cytokines-mediated NO production, iNOS expression, and invasiveness of HT-29 cells. These results provide sufficient information for the further development of COS as an antitumor metastatic agent for the treatment of colon cancer.